Articulated Boom Lifting Arrangement

ABSTRACT

A bell crank and a mechanical link are included in an aerial lift system to mechanically constrain motion of a two-boom aerial lift mechanism to prevent the aerial lift system from accessing unstable positions. Typically an aerial lift is coupled to a vehicle via a turntable. The turntable includes a counterweight on a rearward side of the turntable to balance the booms and associated hardware as they are extended in a forward direction. If the booms are in certain rearward, or even vertical positions, the counterweight can cause the vehicle to tip and such unstable positions are to be avoided. By providing the bell crank proximate the pivot joint between upper and lower booms, with the bell crank coupling at pivot joints with: the lower boom, the mechanical link, and an upper hydraulic cylinder, the booms of the aerial lift system are mechanically constrained to avoid vehicle tipping.

BACKGROUND

1. Technical Field

The present disclosure relates to aerial lift systems and vehicles provided with such lift systems.

2. Background Art

One type of aerial lift includes a vehicle onto which a pivotable turntable is mounted, with the turntable having a series of adjustable, and possibly, extendable booms onto which a platform or basket is mounted. Typically, a lower and an upper boom are used to position a platform or basket away from the vehicle to a desired location so that a person within the basket or platform may perform work or maintenance on an object that is otherwise difficult to access.

It is desirable for the boom to allow the basket to extend beyond the footprint of the vehicle. However, as the basket moves with respect to the vehicle, the center of mass of the vehicle system, i.e., including the boom, basket, the person or persons in the basket and whatever other cargo is in the basket, migrates. Several measures can be taken to overcome a tendency of the vehicle to tip when the boom is extended away from the vehicle.

For example, the weight and/or footprint of the vehicle are increased so that the vehicle system is more stable. However, it is undesirable to increase the weight of the vehicle because it makes transporting the vehicle to a work site that much more difficult. Also, if the surface near the work site is unstable, such as may result from a presence of sand or mud, the more that the vehicle system weighs, the more likely the vehicle will become stuck during maneuvering. Another measure used to stabilize the vehicle in the elevated position calls for increasing the track width and/or the wheel base, whereby the foot print of the vehicle is increased, which improves stability. However, the larger the footprint, the less maneuverable the vehicle becomes. Also, a wider vehicle is prevented from accessing certain locations that it may have otherwise been able to access.

Another commonly employed measure involves providing a counterweight on the turntable so that the counterweight rotates with the turntable. The counterweight balances the boom extending in a direction away from the counterweight, which is called a “forward” direction regardless of the angle of the rotation of the turntable. Thus, the forward and rearward directions are defined with respect to the turntable, not with respect to the vehicle or any object that is being accessed from the basket. However, the counterweight provides an undesirable imbalance force when the upper boom is rotated in a rearward direction. Thus, this measure commonly includes taking additional measures to prevent the boom from moving too far rearward.

In some other designs, the positions of the booms are controlled by hydraulic cylinders. By knowing the extent that the hydraulic cylinders are extended, the combinations of boom positions leading to tipping can be avoided. However, such a system relies on having sensors to measure positions of the hydraulic cylinders, a controller, and frequent calibration of the sensors to ensure sufficient measurement accuracy.

In yet another prior design, an upright member is provided between the lower and upper booms. The upright is actively controlled via hydraulic feedback to maintain it in a vertical position. A disadvantage of such a system is that it requires additional hydraulic cylinders managed by complex valving and additional sensors. Furthermore, the system may require periodic calibration. Also, by introducing an intermediate link, i.e., the upright, additional play is introduced. The amount of play is exacerbated at the operator's station in the ‘basket. Such play undermines the operator's sense of security.

SUMMARY

To solve at least one problem in the prior art, an aerial lift system is disclosed which includes a vehicle, a turntable coupled to the vehicle, a lower boom coupled to the turntable at a first turntable pivot, a lower linear actuator coupled between the turntable and the lower boom, and a mechanical link coupled to the turntable at a second turntable pivot. The turntable is coupled to the vehicle with an axis of rotation of the turntable being substantially vertical. The upper side of the turntable includes pivot joints for at least a lower boom and a mechanical link. The axis of rotation about these first turntable and second turntable pivots, in some embodiments, is substantially perpendicular to the axis of rotation of the turntable with respect to the vehicle. A bell crank is coupled to: the lower boom at a first bell-crank pivot and to the mechanical link at a second bell-crank pivot. The system includes an upper boom coupled to the lower boom at a boom-to-boom pivot. The system also includes an upper linear actuator coupled to the bell crank at a third bell crank pivot and coupled to the upper boom. The linear actuators are any suitable linear actuator such a hydraulic cylinder. The mechanical link, in some embodiments, includes two members. The lower linear actuator passes between the two members of the mechanical link as it couples between the lower boom and the turntable.

By providing the mechanical link and the bell crank, the upper and lower booms are constrained in such a manner that they are prevented from accessing positions in which vehicle tipping may occur. This presents advantages over prior designs. For example, in one embodiment of the invention in which the lower boom is coupled to the upper boom, there are fewer pivot points than some prior art systems. Thus, there is less play in the system at the operator basket, which may extend 50 feet or more from the vehicle, during positioning of the basket or due to the wind acting upon the basket. The operator feels more secure and comfortable when the basket bounces to a lesser degree.

At least one embodiment of the invention obviates the need for complicated electronic/hydraulic control and hydraulic actuators used to limit rear instability. Furthermore, the mechanical system does not need calibration, as needed with a system using control valves and actuators. Furthermore, service intervals for some embodiments of the invention described by the present disclosure, which are mechanically based, are likely longer than service intervals for prior systems which may include sensors, controllers, and complex valving.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an aerial lift system in which the booms are in a stowed position for transportation and in which the upper and lower hydraulic cylinders are fully retracted;

FIG. 2 shows an aerial lift in which the upper hydraulic cylinder is fully extended and the lower hydraulic cylinder is fully retracted;

FIG. 3 shows an aerial lift in which the upper and lower hydraulic cylinders are fully extended; and

FIG. 4 shows an aerial lift in which the upper hydraulic cylinder is fully retracted and the lower hydraulic cylinder is fully extended.

DETAILED DESCRIPTION

As shown in FIGS. 1 through 4, an aerial lift system 10 includes a vehicle 12 with an aerial lift 13. According to the embodiment depicted in FIG. 1, vehicle 12 is a wheeled vehicle. Alternatively, vehicle 12 may be a tracked vehicle. In some embodiments, vehicle 12 is not self-propelled. A turntable 14 is rotatably mounted on vehicle 12. Alternatively, element 14 is a support member which is fixed to vehicle 12. A lower boom 16 is coupled to turntable 14 via a pivot joint 18, at or near to a proximal end of the lower boom 16. A lower hydraulic cylinder 20 is pivotally coupled between turntable 14 and lower boom 16. Generally, a distal end of the lower hydraulic cylinder 20 is coupled to the lower boom 16 at some distance from the proximal end of the boom 16.

In one embodiment, a proximal end of the lower hydraulic cylinder 20 extends through a slot in turntable 14 to provide stowage space for lower hydraulic cylinder 20. Lower hydraulic cylinder 20 is trunnion that is in turn mounted to the turntable in one embodiment, with the trunnion joint being located along the body of lower hydraulic cylinder 20, i.e., not connected at the proximal end of lower hydraulic cylinder 20. A mechanical link 22 is also coupled to turntable 14 via a pivot joint 23. In one embodiment, mechanical link 22 comprises two members 24 and 26. In the embodiment shown in FIG. 1, lower hydraulic cylinder 20 passes between members 24 and 26 of mechanical link 22. A second end of lower boom 16 pivotally couples with an upper boom 28 at a pivot 29

According to one embodiment, aerial lift 13 includes a bell crank 30 which is pivotally coupled to mechanical link 22 and lower boom 16. Bell crank 30 is also pivotally coupled to an upper hydraulic cylinder 32 at one end of the upper hydraulic cylinder with the other end of upper hydraulic cylinder 32 coupled to upper boom 28. Upper hydraulic cylinder 32 couples with upper boom 28 away from either end of upper boom 28. Upper boom 28 is coupled to lower boom 16 at a close end of upper boom 28. At a far end of upper boom 28, a basket assembly 34 is coupled. Basket assembly 34 includes a platform and/or cage in which an operator, and possibly tools and/or cargo, may be lifted. Basket assembly 34 includes pivotal links and hydraulic cylinders so that it may be raised, lowered, extended, etc. with respect to the far end of the upper boom 28. Furthermore, basket assembly 34 may include components to provide users with automated, or semi-automated, leveling to ensure that basket assembly 34 remains substantially level. In the embodiment shown in FIG. 1, an extendible link 36 is provided between the basket assembly 34 and the upper boom 28. The extendible link 36 provides users with apparatus for extending a length of the upper boom 28, and thus extending a reach of the basket assembly 34.

A counterweight 38 (shown in FIGS. 2-4), may be included. In some embodiments, counterweight 38 has a counterweight portion located on both sides of the lower boom 16. For illustration purposes, only the counterweight portion behind lower boom 16 is shown in FIGS. 2-4.

In the preceding paragraphs, embodiments showing some of the elements of the present invention have been described. In the succeeding discussion, the system characteristics leading to improved operation are described in regards to FIGS. 2-4, in which the aerial lift is shown with the hydraulic cylinders in extreme positions.

In FIG. 2, upper hydraulic cylinder 32 is shown in a fully extended position while lower hydraulic cylinder 20 is shown in a fully retracted position. In practice, upper boom 28 and lower boom 16 can be adjusted to position basket assembly 34 close to the desired location, i.e., rough location. To more finely adjust the basket to placement into the desired location, basket assembly 34 can be raised, lowered, and rotated independently of upper boom 28 and lower boom 16. As shown in FIG. 2, basket assembly 34 is in a lower position, but can be raised as needed to obtain further height above vehicle 12.

Generally, bell crank 30 has three pivots: a lower boom pivot 30 a, a mechanical link pivot 30 b, and an upper hydraulic cylinder pivot 30 c. As shown in FIG. 2, upper hydraulic cylinder pivot 30 c is below mechanical link 22. This limits the extent to which upper hydraulic cylinder 32 can extend and thus limits the rotation of upper boom 28 in the rearward direction.

In FIG. 3, both upper hydraulic cylinder 32 and lower hydraulic cylinder 20 are shown in their fully extended positions, i.e., a mostly vertical position. As discussed above, basket assembly 34 can be raised from the position shown in FIG. 3 to attain a slightly higher end position. Furthermore, extendible link 36 can be extended to its furthest position. When lower hydraulic cylinder 20 is extended, lower boom 16 is caused to rotate about pivot joint 18. Lower boom 16 acts on bell crank 30, the motion of which is constrained by being coupled to mechanical link 22. The pivot joint of bell crank 30, which is coupled to upper hydraulic cylinder 32, is rotated so that it is in the interior of the obtuse angle formed between upper boom 28 and lower boom 16.

In FIG. 2, the angle between lower boom 16 and upper boom 28 is about 45 degrees; whereas, in FIG. 3, the angle between lower boom 16 and upper boom 28 is about 135 degrees. In both FIGS. 2 and 3, upper hydraulic cylinder 32 is fully extended. It is the position of bell crank 30, as influenced by the position of lower boom 16 and mechanical link 22, which causes the different relative positions of the two booms. The relative angle between the two booms, described in regards to FIGS. 2 and 3, is not intended to be limiting, but is provided instead for illustrative purposes only. The relative lengths of the booms, the mounting positions of the hydraulic cylinders on the booms, the size and location of the pivot joints on the bell crank, the position of the mechanical link in relation to the lower boom, the extensions of the hydraulic cylinders, and other parameters are parameters which influence the angle in between the booms. Many alternative combinations of such parameters are within the scope of the present disclosure and many would provide for other angles between the booms.

In FIG. 3, hydraulic lines 40 and 42 are shown coupled to bosses 41 and 43 on upper hydraulic cylinder 32. Bosses 41 and 43 and hydraulic lines 40 and 42 are not shown in FIGS. 1, 2, and 4 for illustration simplicity. When supplying fluid via hydraulic line 40, the upper hydraulic cylinder 32 extends. When supplying fluid via hydraulic line 42, the upper hydraulic cylinder 32 contracts. Lower hydraulic cylinder 20 has analogous hydraulic lines 44 and 46. A lower operator-controlled actuator 48 and an upper operator-controlled actuator 50 may be provided for operation from within the basket assembly 34. In one embodiment, actuators 48 and 50 are push-pull levers. Actuators 48 and 50 control hydraulic pressure supplied in lines 40, 42, 44, and 46. Other embodiments, including electronically actuated actuators, may be used.

In FIG. 4, the combination of lower hydraulic cylinder 20 fully extended and upper hydraulic cylinder 32 fully retracted is shown. Bell crank 30 is in the same position in FIG. 4 as in FIG. 3. Both FIGS. 3 and 4 show lower boom 16 in the furthest forward position accessible (which is approximately 25 degrees rotated toward the rearward direction from a vertical axis in the embodiments shown in FIGS. 3 and 4). With upper hydraulic cylinder 32 fully retracted, this shows a position in which basket assembly 34 is far forward. In this example, counterweight 38 counterbalances the weight of basket assembly 34, upper boom 28, and whatever cargo is in basket assembly 34.

Combinations of the extreme positions of hydraulic cylinders 20 and 32 are shown in FIGS. 1-4. Bell crank 30 and mechanical link 22 influence the range of motion of the lower boom 16 and upper boom 28 such that a significant range of motion is provided in such positions illustrated in FIGS. 1-4 as well as intermediate positions of cylinders 20 and 32. However, bell crank 30 and mechanical link 22 inhibit accessing unstable positions of the aerial lift system, i.e., positions potentially leading to vehicle tipping.

By adding bell crank 30 and mechanical link 22, as shown in FIGS. 1-4, aerial lift 13 is prevented from accessing rearward positions that might result in the vehicle tipping. The disclosed system provides an advantage over prior art systems in that vehicle tipping is prevented by a purely mechanical system . In prior art systems, at least position sensors and a control system are used to ensure that tipping positions are not accessed. Such systems depend on the sensors providing an accurate measurement to the control system, and the control system maintaining control over the hydraulic cylinders. According to embodiments of the present invention, tipping is prevented without relying on sensors and actuators.

According to embodiments of the present disclosure, upper boom 28 and lower boom 16 are directly linked with their range of motion controlled via hydraulic cylinders, 20 and 32, mechanical link 22, and bell crank 30. In some prior art systems, an additional link is included between upper and lower booms. As each link between the turntable and the basket adds to the amount of play experienced at the basket, it is an advantage, according to some embodiments of the present disclosure, that no such additional link is employed.

Another advantage, according to the present disclosure, is that the operator can directly control hydraulic cylinders 20 and 32 without relying on an electronic controller. In some prior art systems, a controller is interposed between operator controls and linear actuators to ensure that undesirable positions of associated booms are not accessed. In other prior systems, an additional link is provided between upper and lower booms and a complex control scheme is employed to ensure that undesirable positions are not accessed.

While the best mode has been described in detail, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. For example, hydraulic cylinders 20 and 32 are shown in FIGS. 1-4. However, any type of linear actuator, such as electro-mechanical motors (such as a stepper motor), a linear motor, etc. can be used in place of hydraulic cylinders. Where one or more embodiments have been described as providing advantages or being preferred over other embodiments and/or over prior art in regard to one or more desired characteristics, one of ordinary skill in the art will recognize that compromises, additions, subtractions or other modifications may be made among various features to achieve desired system attributes, which may depend on the specific application or implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described as being less desirable relative to other embodiments with respect to one or more characteristics are not outside the scope of the disclosure as claimed. 

1. A boom system, comprising: a support member; a lower boom coupled to the support member at a first turntable pivot; a lower linear actuator coupled between the support member and the lower boom; a mechanical link coupled to the support member at a second support member pivot; a bell crank comprising: a first bell-crank pivot coupled to the lower boom; a second bell-crank pivot coupled to the mechanical link; and a third bell-crank pivot; an upper boom coupled to the lower boom via a boom-to-boom pivot; and an upper linear actuator coupled to the bell crank at the third bell crank pivot and coupled to the upper boom.
 2. The boom system of claim 1 wherein the bell crank is generally triangular with the first, second, and third bell crank pivots located near corners of the generally triangular bell crank.
 3. The boom system of claim 1 wherein the support member is a rotatable turntable, the lower boom couples with the turntable proximate a first end of the lower boom, the lower boom couples with the upper boom and the bell crank proximate a second end of the lower boom, and the lower linear actuator couples with the lower boom at a point in between the first and second ends of the lower boom.
 4. The boom system of claim 1 wherein the lower linear actuator is pivotally coupled to the lower boom at a coupling location and the coupling location is proximate a first end of the lower linear actuator and along the length of the lower boom.
 5. The boom system of claim 4 wherein the support member is a turntable, a second end of the lower linear actuator extends through a slot in the turntable, the lower linear actuator is trunnion mounted to the turntable at a location away from the second end of the lower linear actuator, and the lower linear actuator is configured to pivot with respect to the turntable.
 6. The boom system of claim 1 wherein the lower linear actuator is a lower hydraulic cylinder and the upper linear actuator is an upper hydraulic cylinder.
 7. The boom system of claim 6, further comprising: a lower hydraulic line coupled to the lower hydraulic cylinder; an upper hydraulic line coupled to the upper hydraulic cylinder; a lower operator-controlled actuator to control supply of hydraulic fluid in the lower hydraulic line; and an upper operator-controlled actuator to control supply of hydraulic fluid in the upper hydraulic line.
 8. The boom system of claim 1 wherein the support member is a turntable, the lower boom is coupled to the turntable at a first end of the lower boom and the boom-to-boom pivot is located proximate a second end of the lower boom and proximate a first end of the upper boom.
 9. The boom system of claim 8, further comprising a basket system coupled to the upper boom at a second end of the upper boom.
 10. A boom system, comprising: a turntable; a lower boom pivotally coupled to the turntable; a lower linear actuator pivotally coupled between the turntable and the lower boom; a mechanical link pivotally coupled to the turntable; a bell crank pivotally coupled to the lower boom and the mechanical link; an upper boom pivotally coupled to the lower boom; and an upper linear actuator pivotally coupled between the bell crank and the upper boom.
 11. The boom system of claim 10 wherein the lower linear actuator comprises a hydraulic cylinder and the upper linear actuator comprises a hydraulic cylinder.
 12. The boom system of claim 10 wherein the lower linear actuator is coupled to the turntable rearward of a coupling between the lower boom and the turntable, the system further comprising: a counterweight mounted on the turntable, the counterweight located rearward with respect to the coupling between the lower boom and the turntable.
 13. The boom system of claim 10 wherein: the mechanical link is coupled to the turntable at a location that is rearward with respect to a coupling between the lower boom and the turntable; and the lower linear actuator is coupled to the turntable at a location that is rearward with respect to a coupling between the mechanical link and the turntable.
 14. The boom system of claim 10 wherein the mechanical link comprises two members and the lower linear actuator passes through the two members of the mechanical link.
 15. The boom system of claim 10 wherein one end of the lower linear actuator extends through an opening in the turntable.
 16. The boom system of claim 15 wherein the lower linear actuator is trunnion coupled to the turntable, the lower linear actuator is a hydraulic cylinder, and the upper linear actuator is a hydraulic cylinder.
 17. An aerial lift system, comprising: a vehicle; a turntable rotably coupled to the vehicle; a lower boom pivotally coupled to the turntable; a mechanical link pivotally coupled to the turntable; a bell crank pivotally coupled to the lower boom and the mechanical link; and an upper boom pivotally coupled to the lower boom.
 18. The aerial lift system of claim 17, further comprising: a lower hydraulic cylinder pivotally coupled between the turntable and the lower boom; and an upper hydraulic cylinder pivotally coupled between the bell crank and the upper boom.
 19. The aerial lift system of claim 18 wherein the bell crank is generally triangular with a lower boom pivot proximate a first corner of the bell crank, a mechanical link pivot proximate a second corner of the bell crank, and an upper hydraulic cylinder pivot proximate a third corner of the bell crank.
 20. The aerial lift system of claim 17, further comprising: an extendible link coupled to the upper boom; and a basket system coupled to the extendible link. 